What A Difference A Lifetime Makes
by hushedgreylily
Summary: All those memories. All that history. Addison remembers. SPOILERS. Maddek oneshot.


**WHAT A DIFFERENCE A LIFETIME MAKES**

 **So Shonda killed Derek. And Amelia would have phoned Addie, and Derek was such a huge part of her life she would have had a huge story.**

 _When Addison looks at her cell, she's got five missed calls. She starts panicking when she notices they're all from Amelia._

 _She dials her number, heart thudding. Amelia's been so well for so long, now._

 _Addison's missed having her in LA, but she figures she's in the right place. Where she needs to be._

 _The cell keeps ringing, seemingly infinitely._

 _Amelia finally answers._

" _Dr Shepherd." The other voice sounds shaky._

" _It's Addison."_

 _What she hears next sounds somewhere between a sob and Amelia being strangled._

" _He's dead, Addie."_

 _There's some sort of dull, cold, seeping dread._

" _Breathe, Amelia. Who's dead?"_

" _Derek." She whispers, as if she's suddenly afraid to say. "My brother."_

* * *

She met Derek over a carcass in the dissection lab that first semester at med-school, and Mark that evening at the local student bar after she agreed to go out for drinks with Derek and 'a couple of his friends'. Turns out a couple of his friends turned into only Mark, and within hours of meeting one and only minutes of meeting the other, she was sat between them, vodka shots lined up, laughing.

That didn't change for a long time.

That first summer, before she was even really part of Addison-and-Derek, and a long time before she even thought Addison-and-Mark was the slightest possibility, they went to her parent's cabin by the lake, with Savvy, Naomi and Sam. They spent most of their days sleeping and most of their evenings drinking, and very little time purely _absorbing_ how beautiful the lake was in summer.

Except for one night. One night the three of them wandered down to the shore as the sun set. Sam was still feeling the hangover from yesterday's antics, Savvy and Naomi were painting each other's toe nails, and Addison had fancied a walk. Both Derek and Mark had jumped to join her, and maybe that was slightly pre-emptive of everything that would follow. But that evening, by the lake, they just walked.

They didn't say a lot, walking mostly in some sort of companionable silence. Derek skimmed the tips of his fingers over the long grass, concentrating on the moment and how _right_ the three of them felt, there, together.

They all three sunk into the dirt, once they'd found a gap in the reeds, their toes almost in the water, and looked up at the setting sun.

"I could be here forever." Derek breathed, as the edge of the sun touched on the horizon.

"So could I." Addison responded, looking up at him with a somehow private smile, with something of a foreshadowing.

"We wouldn't survive for long." Mark chuckled, leaning back, resting his elbows in the grass. "We haven't got anything to eat and I don't think we should drink the lake water…"

Addison rolled her eyes, tilting her head back at him slightly. "Oh, shush." She mocked softly, a smile sneaking onto her lips. "It's beautiful."

"That it is." Mark breathed.

The sun went down.

* * *

 _Addison can't think, she can hardly even breathe._

" _I'll get the next flight I can." She half-whispers. "I'll be there."_

" _You don't have to, I-"_

" _I loved him once." Is all she gives in return. It seems so long ago, now, that she'd been half of Derek-and-Addison, and moments ago at the same time. The nausea rises in her throat. "I'm coming to Seattle."_

" _I didn't know who else to call." Amelia sounds like a child, then._

" _I was married to him for eleven years, Amelia."_

 _ **Eleven years.**_ _He'd been the most important person in her life for at least ten of those. Addison can't breathe._

* * *

Derek kissed Addison one night after a few too many glasses of wine; after that, neither of them looked back for a long time. Mark didn't seem to mind, and it didn't seem to make anything all that different when it was the three of them. Because they'd been friends before there had been anything floating between them, and those had been simpler times. It didn't seem like there was any reason they weren't all three going to stay friends.

Sometimes Mark's significant other of the week was with them, sometimes it was just the three of them. It didn't seem to matter. They were something of a family.

He was perfect, in those years. He came to all the Montgomery family gatherings, in all their glory, and he smiled and said exactly the right things to make Bizzy smile and the Captain approve; somehow prim, proper, intelligent.

He was anything but prim and proper when he snuck across the hallways of the Montgomery house in those nights, creeping between her bed sheets and driving her to bite down on the pillow to stop herself screaming.

He'd sneak out before anyone woke in the morning, and would make barely discernible eyes at her across the breakfast table, as conversation was proper and intelligent again.

It was thrilling, those years. He was her perfect-on-paper, slightly-darker-in-private, almost-a-doctor boyfriend. Bizzy and the Captain seemed to step back a little for the first time in her life, and she gauged from Archer's cocked eyebrow assessment that either he was happy that Derek was looking after her, or was sure that Derek wasn't any kind of a threat (you could never be sure with Archer, it was probably dependent on his mood), and he backed off too. She suddenly felt like she had all the freedom in the world, and in those days she was sure she and Derek were going to last forever; the whole of the rest of her life was suddenly both in her hands and looking _beautiful._ And, with hindsight, she had Derek to thank for most of that.

The night after their graduation ceremony, after what was, unbeknownst to them, the last party quite like that of their lifetimes, they headed up to the room they were staying in the new Four Seasons Hotel. She was tired, she'd had to hold Naomi's hair back as she'd thrown up into the toilet, following a nasty row with Sam, and she'd had to have stern words with Mark, getting hot and heavy in the corner with one of their classmates' younger sister, who had looked barely out of high school and had a very threatening looking father. And she'd opened the door to their room (neither Bizzy, Archer nor the Captain would have approved if they'd known she was sharing a hotel room with Derek that night, despite them having been together four years), she was assaulted by the gentle scent of burning incense, candles all around the room, and two glasses of cold white wine set on the balcony table.

She stopped for a moment, absorbing the surroundings. Derek, slightly shakily, more nervous than she thought she'd seen him in years, led her out onto the slightly-too-cool-to-be-out-there-for-long balcony.

There were two freshly poured glasses of wine on the little balcony table, and a small red velvet box. She suddenly couldn't breathe, couldn't hardly move. This was her fairy tale.

His voice was slightly shaky as he kept one of her hands in his and lifted the red box; his hands were shaking as he lifted the lid, and he wouldn't meet her eyes.

He took an almost comically visible deep breath and looked at her, and in that moment there were a thousand possible futures in his eyes. She was sure her heart got as close to skipping a beat as was possible.

"These last four years, Addie, they've been…" he trailed off, staring into the little box.

"Wonderful?"

Relief seemed to flood his face, as if he'd been doubting she was on the same page as him.

"Wonderful." He agreed, a new certainty in his voice. He inhaled deeply again, and took something out of the box. Then his fingers were sliding out of hers, and before she could blink he was kneeling on the floor, a beautiful little gold set ruby in his fingers.  
"Addison Adrianne Forbes Montgomery, will you marry me?"

The street was surprisingly quiet, but all of a sudden there were fireworks exploding somewhere in the distance, and it couldn't have been more fitting. She didn't cry, Montgomerys _don't_ , she'd had that indoctrinated into her from a young age, but the tears were falling off her chin with her frantic nodding, and for a while she didn't feel like a _Montgomery,_ self-sufficient and strong and independent. She felt like the girl in that perfect fairy tale, which despite the last years of happiness she'd never been sure she was going to be a character in. She managed to breathe 'yes' with her nods when she caught her breath, and Derek slipped the ring onto her finger, a smile on his face wider than any she'd ever seen.

He led her back into the warm, fingers still interlaced with hers.

* * *

 _Jake's arms are around her, and she buries her face in his shoulder. Wordlessly, she knows he understands where she is right now._

" _I need to go to Seattle."_

" _I know." There's a sadness in his eyes she can't quite read. It's maybe understanding._

" _I need to book a flight. I don't know how long I'll be."_

 _There's a pause before he speaks, a pause before he's perfect. "Take as long as you need. Henry and I – we'll have some boy time."_

 _She kisses her sleeping son before she leaves._

 _She heads to the airport by herself. One or both of her neighbours might have come with her if Sam hadn't been in Maryland on a conference and Cassie hadn't been still keeping Naomi up all night. Naomi sends her on her way with sad, tired eyes, hugs and useless, empty words._

 _She needs to go alone, anyway. This isn't anyone else's history._

* * *

Just over a year after everything that had happened on the balcony of the Four Seasons, and the struggle through the infamous year of being an intern completed and passed, she could count the weeks, and then the days, and in that moment the hours until she would be walking down that aisle.

She'd been living with Naomi, Sam and a couple of other interns the last year, but Derek and Mark had a flat a few blocks away that she'd been spending more than half her time at. She was in their kitchen now, Naomi by her side, to see them off on Derek's bachelor party night out. Derek, ever organised, was ready beside her before Mark, Sam and the rest of the group.

He took her shoulders in his hands, a warm smile on his face.

"I'll see you tomorrow." He whispered, pressing his lips against hers.

"Not before." She scolded, running her fingers through his always-slightly-wayward dark hair.

He pressed his lips to hers once more before the others were heading into the kitchen, already drinking, clapping Derek on the back and loudly ushering him out of the door.

Mark was the last to leave. She wasn't going to, she hadn't been planning on it, but she pulled him back, catching his hand.

"Take care of him tonight, alright?" she breathed, and sobriety seemed to crash over Mark's features. He appeared to have been more intoxicated by the moment than on any substance. "I need him in one piece and not too hungover in the morning."

Something of a strange little half smile danced across Mark's face, then, something she'd never seen before. She hadn't spent as much time with him – she hadn't spent as much time with _anyone_ that last year, she'd been so busy – even having been spending most of her time at his flat; he had invariably either been in an on-call room at the hospital or with his blonde of the week. But she'd never seen his eyes look quite like _that._

She wasn't sure if the pause was slightly too long before he said anything, but then he spoke and she decided she'd probably imagined it.

"You're getting married tomorrow, Red." (surprisingly, the nickname 'Red' hadn't started being about her hair, but one drunken student night involving her excess vodka consumption and a large puddle of expensive red wine). He swallowed, almost indiscernibly. "I'll have the man of the hour at the church on time, I promise."

When he leant forward then and brushed his lips against her cheek, they shouldn't've burnt.

* * *

 _She sits in the departure lounge, an overnight bag Jake had thrown together between her ankles. She's cold, which is ridiculous, because she lives in LA and she hasn't been cold when she's healthy since she lived in Seattle._

 _Across the room from her, queuing for coffee, a woman is struggling to keep her hands on five children, all looking similar ages. Four girls and one boy._

 _She blinks, and for a moment it's Carolyn Shepherd, Derek and his sisters. She's seen plenty of family photos and had enough experience of all of them together to imagine them young. A family, broken in tragedy, contracting tighter and holding together._

 _Now even more broken. She wraps her arms around herself as she thinks of Carolyn Shepherd. She can understand the horrific gravity even more now she has Henry – how no parent should ever suffer losing a child. And to a woman who had lost her husband so long ago, pulled together and held onto tightly to five children – it's unthinkable._

* * *

They should have been drowning in all their work, all their extending study, but they were so _happy_ in those first years everything seemed to feel lighter. They bought the brownstone only a few months after the wedding and the long honeymoon in the Seychelles, and everything started to feel beautifully _domestic._ They used to take walks in the park, even with a picnic in the summer, they used to go out for drinks dressed up in the evening, Derek looking as dapper as always in black tie, the perfect image of a young, sophisticated couple enjoying life.

Sometimes, when it had been a long week, or even a long day, they'd just collapse together between the sheets, content in just _breathing_ with one another.

Her whole life was mapped out, then. She'd broken free of the Montgomerys as much as she could ever hope to, and she was happy her way – mad crazy busy, still working and devoted to her job, and with the man she'd chosen. Sure, he happened to be approved of by Bizzy and the Captain, but he was her choice. And all of a sudden, that fairy tale didn't feel so far away. They were going to grow old side by side, with one or two children at their feet (and they were going to think about that later. They'd talked about it. They were going to settle into their positions at the hospital, start _delegating_ more before they started thinking about having children), and they were going to live happily ever after.

They saw as much of Mark, when he was around, though he didn't seem to fix himself anywhere _,_ those first few years after qualification. He seemed to _flit_. When he was in the city, they went out on double dates with Mark and whomever he could string along, and they talked about work, where their friends from college were now, work, where they were planning on jetting off to the following summer, work and vague plans for the future. But those vague plans for the future were always huge, in Addison's mind. Because it seemed with every day they were a little less vague, a little more real, and they were really going to happen to her, despite every doubt she'd ever had that she'd live up to being what Bizzy and the Captain wanted her to be. Because it was about what she wanted, now, what she was going to get.

They'd been married nearly nine years when Mark stopped flitting. He moved back into the city, and took a position at their hospital. That was the same year she started counting the minutes, realising that those fairy tales maybe needed to start happening sooner rather than later, the same year Derek took the position of Head of Neurosurgery and started researching for another paper.

That was the year everything started to shift.

* * *

 _The man next to her is asleep almost before the plane takes off, and she's grateful for that when tears arrive unbidden in her eyes only a few moments later. The enormity of everything starts to catch up with her._

 _She'd loved him for a time, a long time now she looks back on it, counting the years through a slightly different filter, one without any bitterness, any bad memories that really_ meant _anything, without needing to put him back in his tiny box._

 _She'd loved him for a huge chunk of her life, and at the end of it, she hadn't treated him accordingly. At the end of it, she hadn't remembered what he'd once meant to her._

 _She should've gotten the chance to tell him that, to apologise._

 _She cries silent, desolate tears for most of the next two and a half hours._

* * *

Somewhere in those last years, she started seeing Mark more than her own husband, and even looking back on it, it wasn't all her fault. Derek had driven a wedge between them and somehow set Mark there too, of his own accord. She understood that he was caught up in his work, she understood how much it meant to him – but once upon a time, in her fairy tale, she'd meant as much. Now it didn't seem he even remembered her all the time. He was brilliant at his job, she knew that, and she was even quite perversely _proud_ of how good a Head of Neurosurgery her husband was, but it was costing too much. And it didn't even seem to be eating away at him, he seemed as happy as he'd ever been; it was their marriage that it was consuming.

She'd grown closer to Mark again since he'd been back, and although he was still something of a manwhore (as she would jokingly and affectionately call him on a regular basis), she thought maybe he'd grown up a bit. He'd _settled,_ in a permanent position, and although he was still living on his own with a different woman in his bed on at least a monthly basis, he was suddenly the sturdy, permanent feature her husband wasn't. He would be dropping into the brownstone for a bite to eat when Derek was sleeping in an on call room, he was dancing with her at hospital functions when her husband was using the time to do 'essential research', he was the first to notice the sniffles and running eyes as her signs of the flu.

He shamelessly continued making excuses for Derek, though, like the ever faithful friend he'd always been.

 _he's very busy, it'll calm down when this research paper's finished…_

 _he didn't want to come home in the early hours of the morning and wake you when you have an early shift…_

 _he's just taken up studying for another fellowship, one only five surgeons in the USA are taking – you should be proud, really, Red._

It was that that tipped the bucket, in the end. It was their wedding anniversary (eleven years) and the night before Derek had acknowledged that he hadn't been around much lately, he knew she put up with a lot, and he'd be in to whisk her out for an expensive meal straight after his shift that evening.

When Mark came through the door, her heart plummeted. She'd been in some sort of denial, those last six months, telling herself this was what marriage was about, this was what they signed up for, this was something they were going to get through. But suddenly the reality of how detached from one another they had become hit her hard, and before Mark even came out with any of his excuses, she burst into tears.

He took a step forward, letting her rest her forehead on his shoulder, running his hand down her back.

"He says to say he'll take you out next weekend. Ben Carson is meeting with the Chief of Surgery this evening, and Derek was hoping to talk to him afterwards about the erythromelalgia research – he's not sure how late it'll be, he'll kip in an on-call room and see you in the morning. It's a once in a lifetime, career changing opportunity for a neurosurgeon-"

"Stop." She hissed, bringing her eyes up to his. "Just stop."

For a moment, he didn't have anything to say. "Red, I-" he started, but she brought a finger to his lips.

"Stop making all these excuses for him. He never makes them himself, Mark! He doesn't see a problem in anything he's doing himself…" All of a sudden, she was acutely aware of being near enough in his arms. "I've been forgettable to him for a long time…"

Something changed in his eyes, then, so subtle it was hardly noticeable, but they were eyes she'd learnt to translate, without even realising it.

"You're anything but forgettable, Red."

She found her eyes locking with his. A memory stirred, then, that alien darkness in his eyes, something she'd seen before. An image that had been so incomprehensible to her at the time she'd discounted it as a reality – the look in his eyes the night before she'd gotten married.

Before she even had time to think about it, her heart was thumping, her breathing suddenly shallow. She knew her eyes were travelling down to his lips and back up to his eyes, which were still darkening, and she was sure hers were mirroring his. His eyes weren't moving, they were locked in hers.

There was something too much of _honesty_ in them. Like he couldn't shut out the fact that she was his best friend's wife, he'd known Derek twice the time he'd known her.

She had to shut that honesty out, somehow.

And his lips looked so inviting, and his eyes, no matter how innocent his intentions, how aware of where his loyalties should lie, were so alluring.

She closed her own eyes somewhere between a wish, a plan and a thousand possibilities. He tasted of many things all at once – everything she'd forgotten her husband had been able to give her, something she'd never even dared think about before, and more than one possible future.

His hands were on her hips, then, and suddenly every inch of his body was pressed against every inch of hers, and she couldn't think. Not anymore. This wasn't the time or place for thinking.

She'd been married eleven years today, and her husband hadn't even sent her a card. And she couldn't remember the last time she'd made his eyes portray what she'd done to the man in her arms right now.

She hadn't felt this _wanted_ in a long time. So she decided to forget. Forget what she was doing, forget that she was married, forget what Mark was to Derek and the unforgivable betrayal they were both about to commit.

He tasted of _passion,_ and all she could think about was breathing.

* * *

 _The hotel's the same hotel she can remember sitting next to Derek on a bed as Mark walked out of the shower, and that's her first mistake. The sudden enormity catches her, and she finds herself sitting against the pillows, burying her head in her hands, sinking into her knees, before she can even register._

 _All those memories, and the two men that were in most of them – they're both gone. And she loved both of them once._

 _She's never known what she believes in, she isn't even able to pray, but there is no possibility in her mind anymore for there not to be something else, somewhere else._

 _She's got to believe Mark's welcoming Derek into his arms somewhere, and Derek's going to finally see his father again._

* * *

In hindsight, the dissolution of her marriage wasn't entirely down to her, but it was certainly exacerbated when Derek found Mark between their bedsheets one night.

And she was a Montgomery, and a traditionalist, and so she tried to make it work for months, when her husband's heart already belonged to another woman, when she had very little to cling on to. She was a believer in the seemingly impossible, if it was _proper_ , and she managed to convince herself they were going to drag themselves back to being that young couple on the balcony of the Four Seasons.

When she finally realised her marriage was over, and the divorce papers were in production, suddenly Mark was by her side, and she took a moment to consider how he was always there when there was no one else for her to fall back on, how he was steadier than he'd ever been, almost her safety blanket.

She supposed it said something about her nature, but she didn't want a safety blanket, she couldn't tear herself away from excitement, and she ruined everything.

He's always been able to tell when she was lying, but he let her go without a fuss. That hurt more than it should have done, the idea that her safety blanket had given up on her.

And then she ran away, because that was what she'd always done.

* * *

 _She gets a taxi to Amelia's flat and stands on the doorstep in the rain, unsure if all the wet on her cheeks is Seattle's weather, or if some might be tears._

 _She hasn't seen Amelia look so_ young _as she does when she finally opens the door, and she takes the girl in her arms straight away, stroking her dark hair and whispering into her shoulder._

" _He's dead, Addie." Amelia finally manages, between broken-sounding sobs, and it only fuels Addison's tears._

 _It's like a whole lifetime's been ripped away._

* * *

She went to Seattle for Mark's funeral. It was a quiet affair, and that had chilled her – despite how many friends Mark had had throughout his life, despite everywhere he'd been, everyone he'd entangled with, she knew almost everyone in the small church.

Afterwards, she found herself sitting on the stairs at the wake, slightly shaking hands around a glass of red wine she couldn't quite bring herself to drink, like it equalled some sort of finality.

Derek wandered into the hallway, and did a slight double take when he saw her there. Wordlessly, he sat beside her.

"Thank you for coming." He broke the silence, and his voice was slightly hoarser than she'd been expecting. "He would have wanted you to be here."

A tiny, almost imperceptible smile touched her lips. "I loved him once." She breathed, unashamedly. Derek looked away for a moment, and then brought his eyes back to hers.

"He loved you too, didn't he?"

With something of an instinct, reached out and took his hand. "We wouldn't've… I wouldn't… We loved each other, Derek. It wouldn't have happened if we hadn't…"

He shook his head slightly at her, but didn't release her fingers. "Sometimes I wish we could go back to that night, the day we met you, Addie, the way the three of us were then… everything got so much more complicated and messy from then on, really."

She shook her head slightly. "Not all of it. We were happy for a long time, you and I, however hard that is to remember now…"

"I know. I just… I don't want to think of all those memories as tainted anymore…"

"I'm sorry, Derek. And Mark was sorry, too. He would have loved to have had you forgive him."

"I forgave him a long time ago." He gave her a slight smile. "All those memories, all that history… and you're happy where you are now, and I'm happy, and Mark was in love… maybe we should agree only to remember the good memories, only when we were happy…"

She leant against his arm as she whispered, "Only when all three of us were happy."

* * *

 _She opens the front door as quietly as she can, it's gone midnight. Jake's standing in the kitchen, that quiet, perfect smile on his face._

" _I've only just got Henry to sleep." He sighs slightly, as she sets her small case down on the floor. "He should be out for a long time, we went to the fairground today. I haven't seen him look so tired in a long time…"_

 _She hopes her eyes show at least half the gratitude she feels in that moment. He gets a bottle out of the refrigerator, looking a little sheepish._

" _Fancy a glass of wine?"_

 _She leans up and kisses him, lightly, blinking furiously as his eyes close, trying to dissipate the tear that's forming. "I've missed you." She leans into his shoulder, just for a second. "I'm just gonna go kiss Henry. I'll be two minutes."_

 _When she reaches his room, she just stands in her son's doorway for a moment. When she presses her lips ever-so-gently to his cheek, for only a moment, a thousand possible futures flash before her._

That baby, that family she and Derek were going to start when they finally got round to it, when they both finally found time for anyone other than themselves…

Ella, threading her and Mark back together from shattered pieces, building some sort of future for them in a backwards, haphazard fashion, finally sealing whatever was between them…

If she'd pulled her marriage back together, the future they might have had...

If Mark had asked her again, sat in her bed in LA when the daughter he'd only just found out he had had practically been offering them a child, if she hadn't finally been on the other side of a rebound...

 _Henry stirs in his sleep, his eyes floating open a little._

" _Shh, go back to sleep." She whispers, tucking the blankets around her son. "I'll see you in the morning."_

 _His eyes drift closed again, and she smiles through the tears that have seemed to become a permanent feature in the last week. She wouldn't take any of those that once were possible futures, not anymore. She's got everything she's ever needed, really, right here._

 _She leaves his door slightly ajar and returns to the kitchen, where Jake has poured out two generous glasses of Sauvignon Blanc. She sits next to him at the breakfast bar, gently clinking her glass against his._

 _He gives her a soft, understanding smile in return._

" _It'll start to feel more… normal…" he tries, putting a hand over hers. She wraps her fingers with his, not looking at him._

" _The first two men I ever loved… The only men I'd ever loved for a long time… they're dead… that's more than 15 years of my life… vanished…"_

 _He holds her whilst she cries._

* * *

They've been friends longer than they can remember, really, despite everything that happened along the road, despite every time they've vowed that this was _it,_ it was _over, nothing was ever going to be the same._ But in the end, they've got through all of that. And that's what it comes down to; everything between them is stronger than anything that ever could have got in the way. In the end, it never seemed possible that they wouldn't have found their way back together, eventually.

They seem to wander for something of an indefinite amount of time, the sun setting behind the lake. Mark slouching slightly, with his hands in his pockets, Derek's fingertips gently brushing through the tips of the long grass. Wordlessly, they sit by the shore of the lake, near the reeds, almost at the water's edge.

Faces dance behind both their eyes. Memories. Women they loved.

Among others, a woman with red hair smiles at both of them.

The sun sinks, slowly, behind the lake, until you can hardly see anything at all.

 **Phew, that was a long haul! I hope I've managed to get the balance right, and I've given you enough Addek along with the Maddison I love.**

 **Because the three of them were so much of each other's lives.**

 **I'm super nervous posting this in the crossover section, worried that it will be unnoticed - let me know what you think, leave a review, however short, however critical (though constructive criticism please).**


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